This invention relates to an exposure apparatus for production of a phosphor screen of a cathode ray tube and more particularly, relates to an exposure apparatus for production of the phosphor screen of multineck color cathode ray tubes.
Recently, for the color display tube with a large-sized screen and a sufficient high degrees of brightness and resolution, a multineck color cathode ray tube has been proposed. For example U.S. Pat. No. 4,714,856 discloses a cathode ray tube, which includes a phosphor screen formed on an inner surface of a single glass panel and 12 electron gun assemblies provided in necks. In accordance with the electron gun assemblies, the phosphor screen has 12 effective areas for reproduction of images. Each electron gun assembly emits three electron beams for bombarding phosphor stripes of red, green and blue formed in the corresponding effective area of the phosphor screen. Deflection yokes are provided outside funnels which connect the necks to the panel, respectively.
During operation of the tube, the electron beams emitted from the electron gun assemblies scan the corresponding effective areas due to the deflection yokes, respectively, and thus images with the high brightness and resolution can be reproduced on the large phosphor screen, entirely.
For formation of such phosphor screen with large size, an exposure apparatus shown in FIG. 1 can be considered. Namely, as an extention of the exposure apparatus used for formation of the phosphor screen with an ordinary size, such as 20 inches-size or the less, the exposure apparatus 1 includes a housing 2 divided into cells 2a, 2b, 2c and 2d, a plurality of light sources 3a, 3b, 3c and 3d, such as a mercury lamp or xenon lamp, for exposing predetermined regions corresponding to the effective areas of the phosphor screen, respectively. Correction lenses 4a, 4b, 4c and 4d and intensity correction filters 5a, 5b, 5c and 5d are placed above the light sources 3a, 3b, 3c and 3d for correct exposure. On the top of the apparatus 1, is placed a panel 6 with a photosensitive layer 7 formed on an inner surface of the panel 6 for forming phosphor stripes of red, green and blue, and light absorbing stripes between the phosphor stripes. A shadow mask 8 is placed inside the panel 6.
Many problems have occurred when the apparatus shown in FIG. 1 is used for formation of the large-sized phosphor screen for the multineck tubes. Namely, it is hard to uniformely form the phosphor stripes and light absorbing stripes in sizes and pitches, since keeping the intensity of all light sources to be constant for a long duration is not easy. Also, since the distance between neighboring light sources are very small, mechanism of cooling system and moving system of the light sources are extremely complicated and required to be accurate.
In Japanese Utility Model Disclosure No. 51-30462, is disclosed an exposure apparatus for formation of the light absorbing stripes coating of the phosphor screen. The apparatus includes a light source, such as a mercury lamp, and three light conductors, each of which is composed of a plurality of optical fibers, for transmitting the lights from the light source. Inlets of the conductors are bundled and placed adjacent to the light source so as to receive the lights from the light source. Outlets of the conductors are disposed at predetermined positions, respectively.
By using the apparatus, since the light absorbing stripes can be formed by only once exposure, the duration of exposure time can be reduced. However, since intensity of the light emitted from the lamp significantly decreases at the point slightly shifted from a center of the lamp where light intensity is maximum value, illuminance amounts emitted from the outlets are different. As the result, the stripes are not formed, uniformly.